Methods and apparatus for power-efficient iris recognition

ABSTRACT

Disclosed herein are systems and methods wherein the iris biometric of an individual person is acquired using a mobile or static device. This acquisition may involve the use of active illumination and repeated use of the camera and processor, as examples. These modules consume considerable power however, and this can significantly reduce battery life. There is a need therefore for a power-efficient iris recognition system.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application is a continuation application of and claims priority toU.S. application Ser. No. 15/107,390, filed Jun. 22, 2016, and entitled“Methods and Systems for Power-Efficient Iris Recognition”, which is anational stage of, and claims priority to and the benefit ofInternational Patent Application No.: PCT/US2014/072175, filed Dec. 23,2014, titled “METHODS AND APPARATUS FOR POWER-EFFICIENT IRISRECOGNITION” which in turn claims priority to U.S. provisionalapplication 61/920,215, filed Dec. 23, 2013, titled “METHODS ANDAPPARATUS FOR POWER-EFFICIENT IRIS RECOGNITION”; U.S. provisionalapplication 61/931,809, filed Jan. 27,2014, titled “METHODS ANDAPPARATUS FOR A COMPACT AWARENESS SENSOR AND CONTROLLER” and U.S.provisional application No. 61/945,961, filed Feb. 28, 2014, titled“EFFICIENT ILLUMINATION CONTROL FOR IRIS RECOGNITION,” all of which arehereby incorporated by reference in their entireties for all purposes.

BACKGROUND

Iris recognition systems typically comprise at least a sensor and anilluminator and these components consume significant power. There istherefore a need for controlling these components in particular ways sothat iris recognition is enabled, while at the same time the averagepower consumed by the components is reduced.

SUMMARY

Embodiments of the present invention include systems and methods forpower-efficient iris recognition. In one example, the system may includean iris acquisition mode determination module that determines theoperating mode of the system. The operating modes may include i) a modewhere it is determined that no iris recognition is possible, ii) a modewhere it is determined that iris recognition is possible but notpreferred, and iii) a mode where it is determined that iris recognitionis possible and preferred. The determination of the modes may be basedon attributes sensed by the system that relate to iris recognition thatmay include the detected position of the eyes, the detected speed of theuser, the detected brightness of the imagery, the detected change in theimagery over time, or the detected physical acceleration of the system.The system may also include at least one of: a sensor power modecontroller, a sensor region of interest controller, an illuminationpower mode controller, an illumination region of interest controller,and a gaze-motion determination module that, in response to the modedetermination, controls or makes use of the sensor and illuminator inparticular ways that enable functionality of the iris recognition systemwhile at the same time reducing the average power consumed by the systemover time.

The system can function by decomposing the iris recognition system intodifferent modes of operation, including those disclosed immediatelyabove. The system is designed such that in each mode of operation thesensor and illuminator are controlled such that just enough of theirfunctionality is enabled so that the system can acquire sufficient datafrom the sensor in order to determine that it is preferable to switch toa different mode of operation of the iris recognition system. The systemis designed such that the overall functionality of the iris recognitionsystem is still enabled despite the switching between the differentmodes of operation. The system is designed such that the sensor andilluminator consume substantially different power levels in each mode,so that the system is highly efficient with regards to power usage overtime. In some embodiments, these power levels may be an ultra-low powerlevel corresponding to the mode where it is determined that no irisrecognition is possible, a low power level corresponding to the modewhere it is determined that iris recognition is possible but notpreferred, and a standard power level corresponding to the mode where itis determined that iris recognition is possible and preferred.

In some embodiments the system adjusts the power consumed by the sensorby adjusting the time period between sensor enablements over time. Forexample, if the sensor is enabled only every 10 seconds, then less poweris consumed overall compared to the power consumed if the sensor wasenabled every 1 second.

In some other embodiments, the system adjusts the power consumed by thesensor by adjusting the spatial window in which that the sensor regionof interest is active, even if the time between enablements is constant.The rate at which pixels are clocked out of a sensor is typically fixed,so that reducing the size of the active spatial window of the sensorreduces the time during which the sensor is enabled, and thereforereduces the average power consumed by the sensor.

The rate of sensor enablement as well as the size of the spatial windowin which the sensor region is active in the different modes are designedso that the performance of the iris recognition system is maintained.

In some other embodiments, the system adjusts the power consumed by theillumination by adjusting the power of the illuminator while in eachmode. The system is designed such that in some modes of operation lessillumination power is required than in others. The system is alsodesigned such that the illumination may be controlled to be at differentbrightness levels during different active spatial windows of the sensor.

In some other embodiments, a gaze-motion measurement module takesadvantage of the sensor and illuminator in the iris recognition system.This avoids the need for a separate gaze-motion measurement module thatwould consume additional power. In addition, the gaze-motion measurementmodule computes the motion of the gaze of the user directly, as opposedto the absolute gaze direction of the user where ill-conditionedtriangulation and calibration methods are required, and the result is arobust, noise-free measurement of gaze motion that leverages the samesensor and illuminator used for iris recognition.

In summary, in some embodiments, the system may comprise: at least onesensor for iris acquisition mode determination and iris recognition, aniris acquisition mode detection module that controls a sensor powercontrol module, at least one of an illumination power control module oran illumination region of interest control module; wherein the irisacquisition mode determination module determines at least one of theconditions: iris recognition is not possible, iris recognition ispossible but not preferred, iris recognition is possible and preferred;wherein the determined iris acquisition mode controls the sensor powercontrol module to adjust the time between enablement of the sensor, andan iris recognition module.

In some other embodiments, the system may comprise: at least one sensorfor iris acquisition mode determination and iris recognition, an irisacquisition mode detection module that controls a sensor region ofinterest control module, at least one of an illumination power controlmodule or an illumination region of interest control module; wherein theiris acquisition mode determination module determines at least one ofthe conditions: iris recognition is not possible, iris recognition ispossible but not preferred, iris recognition is possible and preferred;wherein the determined iris acquisition mode controls a sensor region ofinterest control module to adjust the active pixel region of interest ofthe sensor, and an iris recognition module

In some embodiments the system may operate by making: a determinationthat one or both eyes of the user are detected to be within the imageregion corresponding to the field of view of the illumination used foriris recognition; a determination that the user is detected to be withinthe depth of field of the iris recognition system; a determination thatthe user is detected to be moving at a speed less than a speedthreshold; a determination that the brightness level of the acquiredimage is less than a threshold; a determination that the change detectedbetween images acquired at two or more different times is below athreshold; a determination that a measurement of the acceleration of thedevice from an accelerometer is below a threshold.

In some embodiments, the aforementioned speed threshold is 13.75 cm/sec.

In some embodiments wherein when the iris acquisition mode determinationmodule has determined that the mode is that no iris recognition ispossible, then the time period between sensor enablements is less than20 seconds.

In some embodiments wherein when the iris acquisition mode module hasdetermined that the mode is one of: that iris recognition is possibleand conditions are such that preferred iris imagery may be acquired, orthat iris recognition is possible and conditions are such thatnon-preferred iris imagery may be acquired, then the time period betweensensor enablements is less than 5.5 seconds.

In some embodiments wherein when the iris acquisition mode module hasdetermined that the mode is that no iris recognition is possible, theactive pixel region of interest of the sensor is adjusted to be lessthan the region of interest of the sensor.

In some embodiments wherein the active sensor region of interest isadjusted so that the ratio of the active vertical window to the irisdiameter is equal to or greater than 3.12.

In some embodiments wherein the illumination region of interest controlmodule configures the illumination to illuminate one region of the imagewith a first illumination power and the other regions of the image witha second illumination power to produce a resultant bright and darkbanded image.

In some embodiments the aforementioned bright and dark banded image isprocessed by normalizing the intensities inside the image region ofinterest corresponding to the first illumination power and the imageregion of interest corresponding to the second illumination power.

In some embodiments, the active sensor region of interest is moved overtime so that the combined accumulated active sensor region of interestover time covers a larger area of the sensor region compared to the areaof the region of interest.

In some embodiments, a first sensor configuration is used for irisacquisition mode determination and a second sensor configuration is usedfor iris recognition

In some embodiments that include a gaze-motion detection module, thesystem may comprise: at least one sensor for iris acquisition modedetermination and iris recognition; an iris acquisition mode detectionmodule that controls a sensor power control module; at least one of anillumination power control module or an illumination region of interestcontrol module; wherein the iris acquisition mode determination moduledetermines at least one of the conditions: iris recognition is notpossible, iris recognition is possible but not preferred, irisrecognition is possible and preferred; wherein the determined irisacquisition mode controls the sensor power control module to adjust thetime between enablement of the sensor; an iris recognition module; agaze-motion determination module comprising an alignment module thatdetermines at least one common feature between two or more images of theeye acquired over time and aligns the images to that feature, and amotion detection module that computes the motion of one or moreremaining features in the eye.

In some other embodiments that also include a gaze-motion detectionmodule, the system may comprise: at least one sensor for irisacquisition mode determination and iris recognition; an iris acquisitionmode detection module that controls a sensor region of interest controlmodule; at least one of an illumination power control module or anillumination region of interest control module; wherein the irisacquisition mode determination module determines at least one of theconditions: iris recognition is not possible, iris recognition ispossible but not preferred, iris recognition is possible and preferred;wherein the determined iris acquisition mode controls a sensor region ofinterest control module to adjust the active pixel region of interest ofthe sensor; an iris recognition module; a gaze-motion determinationmodule comprising an alignment module that determines at least onecommon feature between two or more images of the eye acquired over timeand aligns the images to that feature, and a motion detection modulethat computes the motion of one or more remaining features in the eye.

It should be appreciated that all combinations of the foregoing conceptsand additional concepts discussed in greater detail below (provided suchconcepts are not mutually inconsistent) are contemplated as being partof the inventive subject matter disclosed herein. In particular, allcombinations of claimed subject matter appearing at the end of thisdisclosure are contemplated as being part of the inventive subjectmatter disclosed herein. It should also be appreciated that terminologyexplicitly employed herein that also may appear in any disclosureincorporated by reference should be accorded a meaning most consistentwith the particular concepts disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The skilled artisan will understand that the drawings primarily are forillustrative purposes and are not intended to limit the scope of theinventive subject matter described herein. The drawings are notnecessarily to scale; in some instances, various aspects of theinventive subject matter disclosed herein may be shown exaggerated orenlarged in the drawings to facilitate an understanding of differentfeatures. In the drawings, like reference characters generally refer tolike features (e.g., functionally similar and/or structurally similarelements).

FIG. 1 shows a block diagram of the power-efficient iris recognitionsystem, according to some embodiments.

FIG. 2 shows a physical implementation of the power-efficient irisrecognition system, according to some embodiments.

FIG. 3 shows a user positioned in front of the sensor in a position thatis not-preferred for iris recognition, according to some embodiments.

FIG. 4 shows a user positioned in front of the sensor in anotherposition that is not-preferred for iris recognition, according to someembodiments.

FIG. 5 shows a user positioned in front of the sensor in anotherposition that is preferred for iris recognition, according to someembodiments.

FIG. 6 shows the enablement of the sensor over time, and the averagepower consumed by the sensor, for different determined iris acquisitionmodes of operation, according to some embodiments.

FIG. 7 shows the active region of interest window of the sensor overtime, and the average power consumed by the sensor, for differentdetermined iris acquisition modes of operation, according to someembodiments.

FIG. 8 shows a user position in front of a sensor such that the eyes arewithin the active region of interest window of the sensor, according tosome embodiments.

FIG. 9 shows a user positioned in front of a sensor such that the activeregion of interest window of the illumination is changing over theactive region of interest of the sensor such that a portion of theactive region of interest of the sensor is illuminated at a differentbrightness level compared to other portions of the active region ofinterest of the sensor, according to some embodiments.

FIG. 10 shows a user position in front of a sensor such that the activeregion of interest window of the sensor is changing over a time period,according to some embodiments.

FIG. 11 shows an implementation of the system on a mobile phone,according to some embodiments.

FIG. 12 shows a block diagram of the system such that one sensor is usedto determine the iris acquisition mode of operation, and a second sensoris used to perform iris recognition, according to some embodiments.

FIG. 13 shows an implementation of the system in FIG. 12, according tosome embodiments.

FIG. 14 shows, on the left, images acquired by the sensor of a userchanging their gaze between two different time periods, and on the rightmagnified images of the right eye of the user at the two different timeperiods, according to some embodiments.

FIG. 15 shows a block diagram of another embodiment of the gaze motionmeasurement module, according to some embodiments.

FIG. 16 shows an implementation of the gaze detection module in FIG. 15,according to some embodiments.

DETAILED DESCRIPTION

FIG. 1 shows an embodiment of the system. A user 100 is facing a sensor101 that is controlled by a sensor power mode controller 104 and asensor region of interest controller 105. The sensor power modecontroller is capable of placing the sensor into at least two modes: lowpower and standard power modes. In low power mode the sensor may not beable to acquire imagery that is suitable for iris recognition but yetthe sensor can be immediately switched to standard power mode whereimagery can be acquired immediately. The sensor region of interestcontroller is capable of configuring the sensor such that not all of thesensor pixels are enabled and only a windowed region of interest isactive. The read-out rate of the pixels is typically constant in termsof pixels per second, and therefore reducing the number of pixels beingread out reduces the duration that the sensor needs to be in standardpower mode and therefore reduces the power used by the sensor.

The output of the sensor 100 is fed an iris recognition module 103. Anexample of such an iris recognition module is U.S. Pat. No. 5,291,560 byDaugman, which is incorporated herein by reference in its entirety. Theoutput of the sensor 100 is also fed to an iris acquisition modedetermination module 102. The preferred iris acquisition detector moduleprocesses the imagery to control the sensor power mode controller module104 and the sensor region of interest controller 105. The irisacquisition mode determination module 102 also controls an illuminationpower mode control module 107 and an illumination region of interestcontrol module 106. The illumination power mode control module iscapable of controlling an illumination drive module 108 such that theillumination power can be in low-power and standard power modes. Inlow-power mode the illuminator 109 driven by the illumination drivemodule 108 controls the illuminator 109 such that it produces fewerphotons during the integration time of the active sensor pixels comparedto standard illumination power mode and therefore consumes less power.The illumination region of interest control module 106 is capable ofalso controlling the illumination drive module 108 so that theillumination is only enabled during the time that the sensor pixels areactive, in some embodiments.

The iris acquisition mode determination module 102 determines at leasttwo modes: conditions that are preferred for iris image acquisition, andconditions that are not-preferred for iris image acquisition. In someembodiments, a third mode is a condition where there is no possibilityof iris image acquisition.

When conditions are determined to be not-preferred for iris imageacquisition, then the system controls the sensor and illuminators andprocessing such that minimal power is consumed, yet enough data isacquired to make the determination of whether conditions are preferredor not-preferred for iris image acquisition. This means that the systemcan rapidly control the sensor and the illuminators so that preferredimagery for iris recognition is acquired.

The factors that control whether conditions are determined to bepreferred or not-preferred for iris recognition or whether irisrecognition is not possible may be a function of the specifics of theiris recognition module.

The albedo or reflectance of the iris is relatively low compared to thealbedo of the face, and as a result significant power is expended by theillumination to produce enough photons that get reflected off the irisand into the sensor to produce imagery with sufficient signal to noiseratio for robust iris recognition. This may mean that the photons arefocused in a relatively narrow beam that may be +/−10 degree to +/−30degree. The field of view of many camera lenses on mobile phones or onlaptop or other static devices may be much larger, for example +/−45degree to +/−60 degrees. The narrow beam of illumination may be targetedat or near the center of the field of view of the camera. In someembodiments, one factor controlling whether conditions are preferred foriris image acquisition is that one or both eyes of the user are detectedto be within the image region corresponding to the field of view of theillumination.

Another factor relates to the depth of field of the iris recognitionsystem. Due to the low albedo or reflectance of the iris, and due to itsrelatively small size (e.g., approximately 10.5 mm in diameter) the lensused to form the image on the sensor typically has a large aperture andalso has a large magnification in order to image sufficient number ofpixels across the iris for recognition (typically 100-200 pixels). Alarge aperture and large magnification typically corresponds to a smalldepth of field of the optical system of the iris recognition system,which may be 1″-5″ in some embodiments. In some embodiments therefore,one factor controlling whether conditions are preferred for iris imageacquisition is that the user is detected to be within the depth of fieldof the iris recognition system.

Another factor relates to motion blur of the imagery. Due to the lowalbedo and reflectance of the iris, the exposure time of the pixels onthe sensor may be large so that any significant motion of the eye duringthe exposure time results in a blurred image of the iris that is notpreferred for iris recognition. The exposure time may be approximately 4msecs and the iris may be acquired such that it is 100 pixels indiameter. In some embodiments a motion blur of 5 pixels of the iris maybe a limit for successful iris recognition. This then corresponds to alateral motion of the user of 5 pixels over 4 msecs. With a nominal irisdiameter of 1.1 cm, 5 pixels corresponds to lateral user motion of5/100*1.1 cm/4 msecs 13.75 cm/sec. In some embodiments therefore, onefactor controlling whether conditions are preferred for iris imageacquisition is that the user is detected to be moving less than aparticular speed or velocity. In some embodiments a preferred thresholdfor the particular speed or velocity is 13.75 cm/sec. As exposure timesincrease then the preferred threshold reduces proportionately. Forexample, with an exposure time of 8 msecs the preferred threshold is6.875 cm/sec. With an exposure time of 16 msecs, the preferred thresholdis 3.4375 cm/sec. In some embodiments therefore, one factor controllingwhether conditions are preferred for iris image acquisition is that theuser is detected to be moving with a speed less than 13.75 cm/sec. Insome other embodiments, a factor controlling whether conditions arepreferred for iris image acquisition is that the user is detected to bemoving with a speed less than 6,875 cm/sec. In some other embodiments, afactor controlling whether conditions are preferred for iris imageacquisition is that the user is detected to be moving with a speed lessthan 3.4375 cm/sec.

Another factor relates to determining whether there is no possibility ofperforming iris recognition, typically because the device is unused. Ifthe system makes such a determination, then the system may enable anultra-low power mode that consumes less power than the aforementionedlow-power mode, but such that the time to switch between ultra-low powermode to standard power mode is longer than the time is takes to switchbetween low-power to standard power mode. This longer time fromultra-low-power mode to standard mode compared to low-power to standardmode is acceptable in the iris recognition system since the time betweenthe user sitting down or picking up to use the device and the time thatiris recognition is needed far logging on or other authentication istypically longer compared to a user already using a system and the timebetween the user initiating a transaction and needing to perform irisrecognition.

In some embodiments, the system determines whether there is nopossibility of performing iris recognition based on a measurement ofdarkness in the image. In the case of a laptop with a camera mounted onthe screen, if the laptop screen is closed then no iris recognition ispossible since there is no possibility of the camera facing a user.Either a visible or an infra-red camera will be almost in contact withthe keyboard or bottom part of the laptop and will therefore acquiredark images. If the laptop is opened however then the camera may observesome brightness due to the ambient illumination in the environment ordue to the reflection of active illumination from the device off objectsin front of the device.

In some other embodiments, the system determines whether there is apossibility of performing iris recognition based on a measurement ofchange in the image. In the case of a laptop with a camera mounted onthe screen, if the laptop screen is open then either a visible or aninfra-red camera will observe the scene. A user moving in the farvicinity of the device can result in change in the acquired imagery overtime indicating that there is a possibility that iris recognition may berequired imminently. Also, a change in the acquired imagery over timeacquired from a mobile phone indicates that the device is moving andtherefore potentially held by a user, indicating that there is apossibility that iris recognition may be required imminently, as opposedto a mobile device left on a table where the imagery acquired does notchange over time. A measurement from an accelerometer on the device canalso indicate that the device is moving.

In some other embodiments therefore, a factor controlling whetherconditions are such that there is no possibility of iris recognition isthat the brightness level of the acquired image is below a threshold. Insome other embodiments, a factor controlling whether conditions are suchthat there is no possibility of iris recognition is that the changedetected between images acquired over time is below a threshold. In someother embodiments, a factor controlling whether conditions are such thatthere is no possibility of iris recognition is that a measurement of anaccelerometer mounted on the device is below a threshold.

In some embodiments the iris acquisition mode determination module 102determines the aforementioned factors using several methods. Asdescribed previously, in some embodiments, one factor controllingwhether conditions are preferred for iris image acquisition is that oneor both eyes of the user are detected to be within the image regioncorresponding to the field of view of the illumination. This can beperformed by detecting the location of the face in the image. Methodsfor detecting faces are described, for example, in M. Turk, A. Pentland,“Eigenfaces for Recognition,” Journal of Cognitive Neuroscience, Vol. 3,No. 1, 1991, pp. 71-86, which is incorporated herein by reference. Thisrecovers the location of the eyes in the image. In FIGS. 3, 4 and 5, thedotted region within the camera field of view is the region that ispreferred for iris acquisition since it is illuminated as describedpreviously. In FIGS. 3 and 4, the eyes are outside the preferred regionof interest. In FIG. 5, the eyes are, inside the preferred region ofinterest. In FIG. 2, images are acquired using the camera and sensor 200and then face detection process is performed on the processor 201. Thecomparison of the recovered eye positions with the pre-determinedpreferred region of interest for iris recognition is also performed onprocessor 201.

Also as described previously, one factor controlling whether conditionsare preferred for iris image acquisition is that the user is detected tobe within the depth of field of the iris recognition system. This can beperformed by taking the output of the face detector module and bydetermining the scale of the face in pixels based on, for example, therecovered pixel separation of the eyes. The separations of the eyes,nose and mouth are relatively fixed across the human population, andalso the lens used in such an iris recognition system in someembodiments has a fixed focal length. This means that the separation ofthe eyes, for example, can be used to determine a range or distance ofthe user from the device, using a pre-calibrated look up table stored onprocessor 201 that relates eye-pixel-separation to user range in inches.The depth of field and nominal operating range of the system is known inadvance from the optical configuration of the iris recognition systemand this gives a minimum and maximum distance within which imagerypreferred for iris recognition can be acquired. The pre-calibratedlook-up table can therefore be used to determine the scale of the face,for example the eye-separation in pixels, to determine whether the useris between the minimum and maximum distance from the device so thatimagery preferred for iris recognition can be acquired, or lies outsidethe range.

Also as described previously, one factor controlling whether conditionsare preferred for iris image acquisition is that the user is detected tobe moving with a speed less than 13.75 cm/sec, or less than 6.875cm/sec, or less than 3.4375 cm/sec, depending on the exposure time. Thisspeed can be computed by detecting the position of the face using theaforementioned method on successive frames of the system acquired over aknown time interval. The focal length of the lens is fixed and known,the sensor parameters are known and the range of the user can beestimated from the scale of the face as described previously, and thisallows the motion of the user to be computed from the change in pixellocations of the eyes in the image. For example, if the position of theleft eye is detected to change 50 pixels over 0.1 seconds, and thenominal diameter of the iris is 100 pixels corresponding to 1.1 cm, thenthe user is moving at 50/100*1.1 cm/0.1 seconds=5.5 cm/sec.

Also as described previously, a factor controlling whether conditionsare such that there is no possibility of iris recognition is that thebrightness level of the acquired image is below a threshold. This can bedetermined by acquiring imagery from the camera 200 and computing theaverage brightness of the imagery on processor 201. If the averagebrightness is below a threshold then the iris acquisition modedetermination module 102 implemented on processor 201 may determine thatthere is no possibility of iris recognition.

Also as described previously, a factor controlling whether conditionsare such that there is no possibility of iris recognition is that thechange detected between images acquired over time is below a threshold.This can be determined by acquiring at least two images at differenttime periods from the camera 200, by computing the difference of the atleast two images on processor 201 at each pixel, by computing the squareof the difference of the at least two images at each pixel, and byaveraging the resulting squared differenced image. If the average changeor difference is below a threshold then the iris acquisition modedetermination module 102 implemented on processor 201 may determine thatthere is no possibility of iris recognition.

Also as described previously, a factor controlling whether conditionsare such that there is no possibility of iris recognition is that ameasurement of an accelerometer mounted on the device is below athreshold. An accelerometer 204 is connected to the processor 201. Ifthe accelerometer reading is determined by the processor 201 to be belowa threshold, then the system may determine that there is no possibilityof iris recognition.

Returning to FIG. 1, the iris acquisition mode determination module 102sends the mode determination to the sensor region of interest controlmodule 105, the sensor power mode control module 104, the illuminationregion of interest control module 106, and the illumination power modecontrol module 107. These modules configure the sensor and control theilluminator in order to enable different power modes. As discussedpreviously the modes determined may comprise a determination that irisrecognition is not possible, a determination that the conditions foriris recognition are possible but not preferred, and a determinationthat the conditions for iris recognition are possible and preferred.These three modes may correspond to three power configurationscorresponding to ultra-low power, low power and standard powerrespectively. The sensor and illumination power control modules 105,104, 106, 107 receive the mode determination and configure the sensorand the illumination to achieve the various power levels.

As discussed previously, in some embodiments the system has beendesigned such that in ultra-low power mode, less power is consumedcompared to low-power mode, but such that the time to switch betweenultra-low power mode to standard power mode is longer than the time istakes to switch between low-power to standard power mode. This longertime to switch from ultra-low-power mode to standard mode compared tolow-power to standard mode is acceptable in the iris recognition systemsince the time between the user sitting down or picking up to use thedevice and the time that iris recognition is needed for logging on orother authentication is typically longer compared to a user alreadyusing a system and the time between the user initiating a transactionand needing to perform iris recognition.

The sensor region of interest control module 105, the sensor power modecontrol module 104, the illumination region of interest control module106, and the illumination power mode control module 107 are nowdescribed in more detail. These modules are implemented on a processor202 that outputs resulting control signals to the camera sensor 200 andan illumination driver 203 that may comprise a field-effect transistor(FET) that converts illumination control signals into current that inturn drives the illuminator 109.

FIG. 6 shows the operation of the sensor power mode control module 104.The solid line on the top graph shows a signal from the control modulethat enables the sensor. The bottom graph shows an output of the irismode determination module. Modes 1 (602) and 2 (603) in this case maycorrespond to ultra-low power and low-power respectively, or maycorrespond to ultra-low power and standard power respectively, or maycorrespond to low-power and standard power respectively. The sensorpower mode control module 104 enables the sensor periodically. In irisacquisition mode 1, the time period between sensor enablements is T1(600). In iris acquisition mode 2, the time period between sensorenablement is T2 (601), such that T2 is less than T1. The longer thetime is between sensor enablements, then the lower the average power 604that is consumed by the sensor.

In some embodiments, in ultra-low power mode, the time period TU betweenenablements may be less than 20 seconds. This time period typicallyprovides sufficient time between the user sitting down or picking up touse the device and the time that iris recognition is needed for loggingon, for example. In low-power mode, the time period between enablementsmay be determined by computing the likelihood that the system will missdetecting that the conditions for acquiring iris imagery are preferredsince, for example, the user may have moved in and out of the preferredconditions for iris image acquisition between sensor enablements. In oneembodiment, if the width of the portion of the sensor illuminatedsufficiently for iris recognition by the illuminator is 500 pixels, thenat a speed of 500 pixels of lateral motion of the user between sensorenablements, the system will be unable to detect that the user was infact in a condition that was preferred for iris image acquisition sincethe eyes would be detected on one side outside the preferred region andthen detected on the other side outside of the preferred region, andnever detected within the preferred region even though the user waspresent there. In this embodiment therefore, it is therefore preferredto choose a time interval in low power mode that is less than a speed of500 pixels between sensor enablements. If the expected lateral motion ofthe user in front of the device is 1 cm/sec, and the nominal diameter ofthe user's iris is 1.1 cm, and the number of pixels across the iris is100, then the time interval between sensor enablements is(500/100*1.1)/1=5.5 seconds. In some applications, particularly if auser is sitting at a laptop and not holding a mobile device, the speedof the user may be larger requiring that the time period TL betweenenablements in low-power mode to be less than 5.5 seconds. In someembodiments, the time period TS between enablements in standard mode maybe equal to or smaller to the time period TL in low-power mode.

FIG. 7 shows the operation of the sensor region of interest controlmodule 105. For clarity, the effects of the sensor power mode control104 have been removed from the description such that the time T1 (704)between enablements is the same in any power mode. It is to beunderstood however that the different methods of power efficiency due toeach of the modules 104, 105, 106, 107 can be used in combination.

The solid line in the top graph in FIG. 7 shows the time during whichthe sensor is enabled, and the average power used by the sensor assuminga fixed time T1 (704) between sensor enablements as discussed. Thebottom graph shows a determination of the iris acquisition mode. Mode 1(702) may correspond to any power mode, and mode 2 (703) may alsocorrespond to any different power mode. The top graph in FIG. 7 showsthat in mode 1 the sensor has been enabled so that pixels within awindow w1 (700) of the sensor are acquired, and that in mode 2 thepixels with a window w2 (701) of the sensor are acquired. Sensorstypically have the same clockout frequency regardless of the area beingimaged, and therefore the smaller the pixel window being acquired thenthe shorter the duration that the sensor is turned on and the less poweris consumed over time. The solid line in the top graph in FIG. 7 showsthat the active window of the sensor w2 (701) is smaller in mode 2compared to the active window of the sensor w1 (700). The average powerover time consumed by the sensor indicated by the dotted line 705 istherefore less in mode 2 than in mode 1. The effects of modifying thewindow of the sensor on the imagery acquired is shown in FIG. 8. FIG. 8shows a top scan point (TP) (800) and a bottom scan point (BP) (801) andshows that only a portion of the field of view of the sensor is acquiredas may be the case in mode 2 in the example. This can be compared toFIG. 5 where the top scan point (TP) (500) and the bottom scan point(BP) (501) are configured such that the entire image is acquired.

In some embodiments, and referring to FIG. 8, in ultra-low power modethe sensor region of interest controller 105 may configure TP (800) andBP (801) such that only a small portion of the sensor is acquired. Thisis because in the methods described previously for determining the irisacquisition mode, only a smaller portion of the imagery may be requiredfor detecting darkness in the imagery or for detecting changes in theacquired imagery. This is significant if the image sensor has a highresolution and has many pixels. In some embodiments in ultra-low-powermode the number of pixels between TP and BP may be less than 1,000,000pixels.

In some embodiments TP and BP may be configured to depend on the motionor position of the user that has been computed by the methods describepreviously in the iris acquisition mode detector module 102. The activesensor window defined by TP and BP can be controlled by the sensorregion of interest module 105 so that the recovered position of the eyeslie between the top scan point TP and the bottom scan point BP.Therefore TP and BP can be varied over time by module 105 as the usermoves. Due to the time period between image acquisitions, it is possiblethat the user may move so quickly that by the time of the secondacquisition the user's eyes are no longer between the top and bottomscan point. In order to resolve this, the difference between TP and BPis set so that the vertical coverage d2 (801) of the sensor (definedwith respect to a sensor with rows horizontally scanned) on the subjectthat corresponds to a lens of a particular field of view is such thatany expected motion of the user will result in the eyes still beingwithin the region defined by TP and BP. In one embodiment, if theexpected motion of the user is 3.4375 cm/sec with a time period betweensensor enablements of 1 seconds and the iris diameter is 1.1 cm asdiscussed previously, then TP and BP should be configured so that theratio of active vertical window d2 (801) to the iris diameter d1 (802)is equal to or greater than (3.4375/1)/1.1=3.12.

FIG. 9 shows the operation of the illumination region of interestcontrol module. It shows that the illumination is controlled to have asecond power level when the scan point of the image sensor is between P1(902) and P2 (903), and a first power level otherwise. In someembodiments P1 may equal TP (900) and P2 may equal BP (901) such thatthere is no purpose in having illumination outside the active windowregion since the sensor is not acquiring any data during that time. Inthis case the first power level may be zero. In other cases P1 and P2may be controlled such that P1 and P2 lie within and BP such that aregion of interest of the sensor corresponding to be being between P1and P2 is illuminated more than other portions of the sensor. This mayreduce the power used by the illumination by illuminating only the irisarea sufficiently well for iris recognition performed in module 103, andonly illuminating the rest of the face area sufficiently well for modedetermination performed in module 102. The methods for detecting themode have been described previously, and may include darkness detection,change detection and face detection in some embodiments.

In order to detect whether there is change or darkness (two of thefactors determined by the iris acquisition mode determination module 102described previously) relatively little illumination is required by thealgorithms and the illumination can be set to be at a low level.Similarly, the features of the face are coarser in scale than thefeatures of the iris, so that the facial features can be blurredspatially to reduce image noise clue to the lower illumination level yetsuccessful face detection as described earlier can still be performed,in the region where iris imagery is acquired for iris recognition bymodule 103 the illumination may be set at a higher level. The resultantimage however has a bright spatial band due to the increasedillumination that may reduce the performance of same of the modedetection algorithms, such as the face detector. This bright spatialband can be removed by a normalization module that inputs the boundarylocations P1 and P2 corresponding to a change in illumination settingduring an image scan, and an algorithm that performs a normalization ofthe image intensities across the boundaries. The normalization modulemay take the average value of the scan line on one side of the boundaryand the average value of the scan line on the other side of theboundary, take the ratio of the average values, and then normalize theintensities using the computed ratio so that the re-computed averagevalues of the normalized scan lines on either side of the boundary arethe same.

FIG. 10 shows another example of the sensor image region controlleradjusting the sensor region of interest over time such that at one timeinstant the region is defined by TP1 (1000) and BP1 (1001), and at asecond time instant is defined by TP2 (1002) and BP2 (1003) so that overtime the combined sensor region TP1 to BP2 is acquired. The process canbe repeated so that the active window of interest covers some or all ofthe sensor field of view. This allows the location of the eyes to bedetected for iris recognition by the iris recognition module 103 or forthe iris acquisition mode detection module 102 if they move outside theconditions preferred for iris image acquisition.

FIG. 12 shows an embodiment of the system where iris recognition andmode detection are performed by two different sensors. In thisembodiment a first sensor 1200 that is sensitive to ambient illuminationis used to perform iris acquisition mode detection 102 and a secondsensor 101 that is sensitive to infra-red illumination is used toperform iris recognition 103. The ambient illumination is indicated by1201, and the infra-red illumination is indicated by 109. This approachmay have an advantage in that ambient illumination requires no activeillumination and therefore less power is consumed by the system since insome of the modes of operation (such as mode: no iris recognition ispossible) only ambient illumination may be sufficient to performdarkness detection or change detection to switch the system into adifferent mode where iris recognition may be possible. The first andsecond sensors may be co-located in a single pixel array so that somepixels are sensitive to visible illumination while some pixels aresensitive to infra-red illumination. FIG. 13 shows an implementation ofthe system whereby the outputs of both sensors 1300 and 200 respectivelyare fed into a processor module 201 which determines the irisacquisition mode and also performs iris recognition, and also sendscontrol signals to a second processor 202 that performs the detailedsensor region of interest control, sensor power enablement control,illumination region of interest control and illumination brightnesscontrol.

In some embodiments the system also comprises a gaze-motion measurementmodule (111 in FIG. 1). This relates to the power efficiency in the irisrecognition system since the imagery acquired for the purposes of theiris recognition module (103) and the iris acquisition mode detectionmodule (102) and some of the same processing steps may be used by agaze-motion detector module (111) as now described, so that a separategaze-motion detector module is not required and therefore the overallpower of the system is reduced.

FIG. 14 on the left shows a first image of the user's face acquired attime T and a second image acquired at time T+1. The right eye of theuser is indicated by 1401 and 1402, respectively, and these aremagnified for clarity on the right of FIG. 14. The illuminator (109)used for iris acquisition mode detection and for iris recognition cancreate a specularity 1403 and 1407 in the acquired images of the eye.The processing used for iris recognition may compute the location of thepupil/iris boundary 1406. 1404 and the location of the iris/scleraboundary 1408, 1409. Rather than compute the absolute gaze orientationof the user, the motion of the gaze orientation of the user can becomputed. In some embodiments, the motion can be computed by aligningthe pixel location of the specular reflections, and by computing thedifference m (1405) in the location of the pupil/iris boundary. Bycomputing the motion of the gaze directly as opposed to an absolute gazedirection in each case and then subtracting the difference, then theresult is a more stable estimation process, resulting in smoother andmore robust graphical user input control.

A method for detecting the location of the specularities 1403, 1407 isto threshold the image and to compute the centroid of pixels above thethreshold. A method for detecting the location and parameters of thepupil/iris boundaries 1406, 1404 and the iris/sclera boundaries 1408,1409 is to perform a Hough transform to detect the parameters ofcircular shapes in the imagery as described in U.S. Pat. No. 3,069,654which is incorporated herein by reference in its entirety.

CONCLUSION

While various inventive embodiments have been described and illustratedherein, those of ordinary skill in the art will readily envision avariety of other means and/or structures for performing the functionand/or obtaining the results and/or one or more of the advantagesdescribed herein, and each of such variations and/or modifications isdeemed to be within the scope of the inventive embodiments describedherein. More generally, those skilled in the art will readily appreciatethat all parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the inventive teachingsis/are used. Those skilled in the art will recognize, or be able toascertain using no more than routine experimentation, many equivalentsto the specific inventive embodiments described herein. It is,therefore, to be understood that the foregoing embodiments are presentedby way of example only and that, within the scope of the appended claimsand equivalents thereto, inventive embodiments may be practicedotherwise than as specifically described and claimed. Inventiveembodiments of the present disclosure are directed to each individualfeature, system, article material, kit, and/or method described herein.In addition, any combination of two or more such features, systems,articles, materials, kits, and/or methods, if such features, systems,articles, materials, kits, and/or methods are not mutually inconsistent,is included within the inventive scope of the present disclosure.

The above-described embodiments can be implemented in any of numerousways. For example, embodiments of designing and making the couplingstructures and diffractive optical elements disclosed herein may beimplemented using hardware, software or a combination thereof. Whenimplemented in software, the software code can be executed on anysuitable processor or collection of processors, whether provided in asingle computer or distributed among multiple computers.

Further, it should be appreciated that a computer may be embodied in anyof a number of forms, such as a rack-mounted computer, a desktopcomputer, a laptop computer, or a tablet computer. Additionally, acomputer may be embedded in a device not generally regarded as acomputer but with suitable processing capabilities, including a PersonalDigital Assistant (PDA), a smart phone or any other suitable portable orfixed electronic device.

Also, a computer may have one or more input and output devices. Thesedevices can be used, among other things, to present a user interface.Examples of output devices that can be used to provide a user interfaceinclude printers or display screens for visual presentation of outputand speakers or other sound generating devices for audible presentationof output. Examples of input devices that can be used for a userinterface include keyboards, and pointing devices, such as mice, touchpads, and digitizing tablets. As another example, a computer may receiveinput information through speech recognition or in other audible format.

Such computers may be interconnected by one or more networks in anysuitable form, including a local area network or a wide area network,such as an enterprise network, and intelligent network (IN) or theInternet. Such networks may be based on any suitable technology and mayoperate according to any suitable protocol and may include wirelessnetworks, wired networks or fiber optic networks.

The various methods or processes (e.g., of designing and making thecoupling structures and diffractive optical elements disclosed above)outlined herein may be coded as software that is executable on one ormore processors that employ any one of a variety of operating systems orplatforms. Additionally, such software may be written using any of anumber of suitable programming languages and/or programming or scriptingtools, and also may be compiled as executable machine language code orintermediate code that is executed on a framework or virtual machine.

In this respect, various inventive concepts may be embodied as acomputer readable storage medium (or multiple computer readable storagemedia) (e.g., a computer memory, one or more floppy discs, compactdiscs, optical discs, magnetic tapes, flash memories, circuitconfigurations in Field Programmable Gate Arrays or other semiconductordevices, or other non-transitory medium or tangible computer storagemedium) encoded with one or more programs that, when executed on one ormore computers or other processors, perform methods that implement thevarious embodiments of the invention discussed above. The computerreadable medium or media can be transportable, such that the program orprograms stored thereon can be loaded onto one or more differentcomputers or other processors to implement various aspects of thepresent invention as discussed above.

The terms “program” or “software” are used herein in a generic sense torefer to any type of computer code or set of computer-executableinstructions that can be employed to program a computer or otherprocessor to implement various aspects of embodiments as discussedabove. Additionally, it should be appreciated that according to oneaspect, one or more computer programs that when executed perform methodsof the present invention need not reside on a single computer orprocessor, but may be distributed in a modular fashion amongst a numberof different computers or processors to implement various aspects of thepresent invention.

Computer-executable instructions may be in many forms, such as programmodules, executed by one or more computers or other devices. Generally,program modules include routines, programs, objects, components, datastructures, etc. that perform particular tasks or implement particularabstract data types. Typically the functionality of the program modulesmay be combined or distributed as desired in various embodiments.

Also, data structures may be stored in computer-readable media in anysuitable form. For simplicity of illustration, data structures may beshown to have fields that are related through location in the datastructure. Such relationships may likewise be achieved by assigningstorage for the fields with locations in a computer-readable medium thatconvey relationship between the fields. However, any suitable mechanismmay be used to establish a relationship between information in fields ofa data structure, including through the use of pointers, tags or othermechanisms that establish relationship between data elements.

Also, various inventive concepts may be embodied as one or more methods,of which an example has been provided. The acts performed as part of themethod may be ordered in any suitable way. Accordingly, embodiments maybe constructed in which acts are performed in an order different thanillustrated, which may include performing some acts simultaneously, eventhough shown as sequential acts in illustrative embodiments.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e., “one or more” ofthe elements so conjoined. Other elements may optionally be presentother than the elements specifically identified by the “and/or” clause,whether related or unrelated to those elements specifically identified.Thus, as a non-limiting example, a reference to “A and/or B”, when usedin conjunction with open-ended language such as “comprising” can refer,in one embodiment, to A only (optionally including elements other thanB); in another embodiment, to B only (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer in one embodiment, to at least one, optionally including more thanone. A, with no B present (and optionally including elements other thanB); in another embodiment, to at least one, optionally including morethan one, B, with no A present (and optionally including elements otherthan A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively, as set forth in the United States Patent Office Manual ofPatent Examining Procedures, Section 2111.03.

The invention claimed is:
 1. A system for power efficient irisrecognition, the system comprising: a sensor to acquire at least oneimage of an iris of a user; and circuitry operably coupled to thesensor, configured to: provide electrical power to the sensor; determinean operational mode of the system using an output from the sensor, theoperational mode indicative of a feasibility of performing irisrecognition of the user based on the at least one image of the iris; andadjust a time period between successive sensing enablements of thesensor according to the determined operational mode so as to control theelectrical power provided to the sensor.
 2. The system of claim 1wherein the circuitry is configured to set the time period betweensuccessive sensing enablements of the sensor to be less than 20 secondsin response to a determination that the operational mode is indicativethat no iris recognition is possible.
 3. The system of claim 1 whereinthe circuitry is configured to set the time period between successivesensing enablements of the sensor to be less than 5.5 seconds inresponse to a determination that the operational mode is indicative thatiris recognition is possible but preferred or that iris recognition ispossible and preferred.
 4. The system of claim 1 wherein the circuitryis configured to determine the operational mode according to at leastone of: a determination that one or both eyes of the user are detectedto be within a region illuminated by a light source used for irisrecognition; a determination that the user is detected to be within adepth of field of the sensor; a determination that the user is moving ata speed less than a speed threshold; a determination that the brightnesslevel of the at least one image is less than a brightness threshold; adetermination that a change between a first image and a second imageacquired by the sensor is below a change threshold; or a determinationthat an acceleration of the sensor is below an acceleration threshold.5. The system of claim 4 wherein the speed threshold is 13.75 cm/second.6. The system of claim 1 wherein the sensor is configured to move anactive sensor region of interest of the sensor over time so as to imagea region larger than the active sensor region of interest.
 7. The systemof claim 1 wherein the sensor is configured to be in a first sensorconfiguration for iris acquisition mode determination and to be in asecond sensor configuration for iris recognition.
 8. The system of claim1, wherein the circuitry is further configured to: determine at leastone common feature between at least two images of an eye of the useracquired over time and to align the at least two images to the at leastone common feature; and estimate motion of at least one other featuresof the eye.
 9. A system for a power efficient iris recognition, thesystem comprising: at least one sensor to acquire at least one image ofan iris of a user, the at least one sensor having a spatial area ofcoverage; and circuitry operably coupled to the at least one sensor,configured to: determine an operational mode of the system using anoutput from the at least one sensor, the operational mode indicative ofa feasibility of performing iris recognition of the user based on the atleast one image of the iris; and adjust a proportion of the spatial areaof coverage, within which the at least one sensor's sensor pixels areactive, according to the operational mode.
 10. The system of claim 9wherein the circuitry is configured to determine the operational modeaccording to at least one of: a determination that one or both eyes ofthe user are detected to be within a region illuminated by a lightsource used for iris recognition; a determination that the user isdetected to be within a depth of field of the at least one sensor;determination that the user is moving at a speed less than a speedthreshold; a determination that the brightness level of the at least oneimage is less than a brightness threshold; a determination that a changebetween a first image and a second image acquired by the at least onesensor is below a change threshold; or a determination that anacceleration of the at least one sensor is below an accelerationthreshold.
 11. The system of claim 10 wherein the speed threshold is13.75 cm/second.
 12. The system of claim 9 wherein the circuitry isconfigured to adjust the proportion of the spatial area of coverage,within which the at least one sensor's sensor pixels are active, to beless than a region of interest of the at least one sensor in response toa determination that the operational mode is indicative that no irisrecognition is possible.
 13. The system of claim 9 wherein the circuitryis configured to adjust the proportion of the spatial area of coverage,within which the at least one sensor's sensor pixels are active, suchthat the ratio of an active vertical window of the at least one sensorto a diameter of the iris is equal to or greater than 3.12.
 14. Thesystem of claim 9, wherein the circuitry is configured to illuminate afirst region of the image with a first power and a second region of theimage with a second illumination power so as to produce a resultantbright and dark banded image.
 15. The system of claim 14 wherein thecircuitry is configured to process the bright and dark banded image bynormalizing the intensities in the image corresponding to the firstillumination power and the image corresponding to the secondillumination power.
 16. The system of claim 9 wherein the at least onesensor is configured to be in a first sensor configuration for irisacquisition mode determination and to be in a second sensorconfiguration for iris recognition.
 17. The system of claim 9, whereinthe circuitry is configured to: determine at least one common featurebetween at least two images of an eye of the user acquired over time andto align the at least two images to the at least one common feature; andestimate motion of at least one other features of the eye.
 18. A methodfor a power efficient iris recognition, the method comprising:acquiring, by at least one sensor, at least one image of an iris, the atleast one sensor having a spatial area of coverage; determining, by aniris acquisition mode detector operably coupled to the sensor and to theiris recognition engine, an operational mode of the at least one sensorusing an output from the at least one sensor, the operational modeindicative of a feasibility of performing iris recognition based on theat least one image of the iris; and adjusting, by a sensor region ofinterest controller operably coupled to the sensor, a proportion of thespatial area of coverage, within which the at least one sensor's sensorpixels are active, according to the determined operational mode.
 19. Themethod of claim 18, comprising adjusting, by the sensor region ofinterest controller, the proportion of the spatial area of coverage,within which the at least one sensor's sensor pixels are active, to beless than a region of interest of the sensor in response to adetermination that the operational mode is indicative that no irisrecognition is possible.
 20. The method of claim 18, comprisingadjusting, by the sensor region of interest controller, the proportionof the spatial area of coverage, within which the at least one sensor'ssensor pixels are active, such that the ratio of an active verticalwindow of the at least one sensor to a diameter of the iris is equal toor greater than 3.12.